A traditional electroacoustic transducer for use in an audio speaker or a headphone assembly includes a diaphragm vibrating in response to the magnitude and frequency of input analogue signals for generating sound waves. Digital signals from a sound source should be converted into analogue signals before input to the traditional electroacoustic transducer.
A signal converter has been developed that enables an electroacoustic transducer to receive digital signals from a sound source without conversion of the digital signals into analogue signals and drive a diaphragm vibrating in response to the compression or density of digital signals for generating sound waves (See for example PTL 1: Japanese Patent No. 4,883,428).
A headphone assembly including the signal converters disclosed in PTL 1 in a right ear piece and a left ear piece can processes digital signals in all the circuit components from the sound source to the drive units of the electroacoustic transducers.
A traditional headphone assembly includes a first electroacoustic transducer and a second electroacoustic transducer in paired right and left ear pieces, respectively. The first electroacoustic transducer receives signals from a sound source and the second electroacoustic transducer receives signals from the sound source via signal lines disposed between the first and second transducers. The signal lines between the transducers are referred to as a connecting cable. The connecting cable is generally disposed inside or along a head band.
Digital signals, which have been affected by extraneous noise during transmission via signal lines, are generally corrected at the receiver. Digital signals are thus barely affected by extraneous noise. Extraneous noise is derived from extraneous electromagnetic waves reaching the signal lines.
The connecting cable is disposed inside or along a head band. The connecting cable disposed above a user's head is readily affected by extraneous electromagnetic waves or extraneous noise as described above.
In the above-mentioned headphone assembly including these two electroacoustic transducers with the signal converters disclosed in PTL 1, digital signals are transmitted from one of the electroacoustic transducers to the other electroacoustic transducer via the connecting cable. The digital signals are directly input to the other electroacoustic transducer without correction and drive the diaphragm.
The received uncorrected digital signals include extraneous noise, which has invaded through the connecting cable. The signals affected by the extraneous noise, which has invaded during transmission, drive the diaphragm. The generated sound waves are thus affected by the extraneous noise. Although digital signals generally have high noise resistance, digital signals affected by extraneous noise and uncorrected at the receiver may fail to produce high-quality sound.
In the field of electroacoustic transducers, there have been disclosed the solutions to the problems of how to prevent extraneous noise invasion or how to eliminate the effects of extraneous noise. Such traditional solutions however cannot be applied to a novel driving scheme that directly drives a diaphragm with digital signals.
To prevent extraneous noise invasion or to eliminate the effects of extraneous noise in the novel driving scheme, digital input signals should be converted into digital driving signals immediately before application to a diaphragm. Thus, the signal converter is disposed in the immediate vicinity to each of the left and right diaphragm.
This complicates the structure and increases the manufacturing cost. In a headphone assembly based on the novel driving scheme, it is desirable to dispose a single signal converter adjacent to only one of the right and left diaphragms and transmit digital driving signals along a head band.
If the first electroacoustic transducer receives digital signals not affected by noise and the second electroacoustic transducer receives digital signals affected by noise, a difference in sensitivity and/or sound quality occurs between the paired right and left electroacoustic transducers.
Moreover, since digital signals include large amounts of high-frequency components, they may emit large amounts of undesirable radiation waves.